This invention relates to an apparatus and methods for the accurate measurement of fixed lengths of yarn or strand while they are wound onto a take-up reel from an essentially continuous supply source. In particular, the invention pertains to an apparatus and methods for the accurate measurement of lengths of fiber glass yarn or strand wound onto bobbins from forming packages rotating on a twist frame.
For quality control purposes, it is desirable that every bobbin carrying similarly sized yarn or strand (hereinafter called "strand") also contain the same length thereon so that yardage variations among a group of randomly selected bobbins is as small as possible. This is important in the manufacture of fabricated products by customers who use bobbins, for example, to make a beam for the production of woven fabric. The early run-out of one bobbin where several are used in forming a beam will interrupt the production process while a new bobbin is spliced in. Such interruptions are inefficient and costly to a fabric manufacturer.
In commercial applications, it has been common practice in the textile industry to wind as many as 100 or more bobbins on a single twist frame. Each bobbin is fed by a single forming package placed on an individual feed roll or creel. The creels are often driven by means of a common drive mechanism from which they may be independently disengaged. Other twist frames may contain creels that are individually driven. Likewise, the bobbins may be driven individually or through a common drive mechanism. As strand is unwound from each forming package and onto its corresponding bobbin, a twist is usually imparted by means of a rotating traveler.
One method which has been used in the past to measure the length of strand wound onto the bobbin is to simply count the number of revolutions of the forming package or those of the bobbin. This approach, while attractive, is subject to significant error since the effect of forming package shape and buildup of yarn on the bobbin is not taken into consideration. A second method of insuring that each bobbin carries the same length of yarn is to simply run each forming package/bobbin pair for a fixed period of time and rely upon the consistency of each forming package to produce bobbins of uniform yarn length. Still yet, another method by which to more accurately measure the length of yarn wound onto the bobbin is to bring the moving strand in contact with the periphery of a rotatable disc or rim of known diameter as the strand is unwound from the forming package. As the strand advances, the tractive force between it and the rim will cause the rim to rotate so long as contact is maintained. Ideally, the tangential velocity of the rim will equal the lineal velocity of the strand and, therefore, each revolution of the rim will measure off a length of strand equal to its circumference. By counting the number of revolutions of the rim and then multiplying by its circumference, one can determine the total length of strand that has been advanced past the rim and onto the bobbin.
In the case of fine strands, several problems must be overcome in order to use this latter technique. Often, it is necessary to maintain a low axial tension in the strand to prevent breakage and other adverse effects during the twisting process. Another problem involves accurately tracking the motion of the strand so as to minimize the relative slip between it and the rotating rim in order to reflect variations in strand velocity.
As will now be shown, the instant invention minimizes or overcomes entirely most of the problems faced by prior art devices.